A Short Message Service Broadcast Channel (S-BCCH), in the IS-136 rev. 0 specification, is specified for use in sending short point-to-multipoint messages to mobile stations, such as radiotelephones. A maximum number of 15 slots per superframe may be assigned to the S-BCCH logical channel. The S-BCCH is considered as a continuous channel even if more than one slot is allocated to the S-BCCH. The IS-136 rev. 0 specification does not specify particulars of this mode of operation, except for the level 2 reservation of slots within a superframe.
One possible implementation for such a system is as follows. This implementation is similar to that originally set forth in the preliminary IS-136 rev. 0 specification.
The SMS frame can be defined as a sequence of 24 Superframes which are aligned with a Hyperframe (HF) counter. Thus, the number of slots assigned to the SMS frame are 0, 24, 48, 72, depending on how many slots per superframe are assigned to BCCH.
The Hyperframe (HF) counter and a Primary Superframe (SF) indicator can be provided in the DCCH. These two counters together (2*HF Counter+Primary SF indicator) constitute a Superframe counter. A SMS frame is defined to be a single complete cycle (0-23) of the SF counter. The SMS frame is aligned to start at a HF counter value of 0, and also when the Primary Superframe indicator equals 0. The SF counter provides SMS frame synchronization information to the mobile station.
SMS subchannels are defined to allow different repetition cycles for different messages. Each subchannel has its own repetition cycle defined in terms of units of SMS frames. SMS frames are grouped into the SMS subchannels. Within each subchannel, a repetition cycle is defined (in units of SMS frames) with which the SMS broadcast message sequences contained in the SMS sub-channel are repeated. The SMS broadcast subchannel cycle may range from 1 to 64 SMS frames in length. Within each subchannel, the first S-BCCH slot within each SMS frame contains a header that describes the structure of the subchannel. Up to four subchannels may be defined. If more than one subchannel exists, the subchannels are time-multiplexed onto the S-BCCH channel on a SMS frame basis. If a SMS subchannel block is defined to consist of one SMS frame from each subchannel, placed in ascending order of subchannel number, then the multiplexed subchannels can be defined as the repetition of these subchannel blocks. The number of subchannels and the identity of the subchannel to which an SMS frame belongs are specified in the SMS frame header.
According to SMS header information found in the first slot in any SMS frame, the set of messages in SMS(i) may span M(i) number of SMS frames before a cycle is completed. M(i) is the length of the sub-channel cycle. The SMS frame number within the subchannel cycle is referred to as the phase of the subchannel cycle.
A number of different BCCH message categories can be defined. These include Emergency Information messages, Time and Date messages, Overload Class messages, System Identity messages, and Broadcast messages. Each BCCH message typically includes a number of fields of information. These fields can include: a Protocol Discriminator field (2 bits), a Message Type field (6 bits), a SMS Message ID field (8 bits), and a Text Message Data field (8 to 2024 bits).
The Broadcast Message category field is coded to provide a number of different types of message category identifiers. These include, by example, emergency numbers and road-side information, toll gate information, airline departure/arrival information, weather-related information, news, and financial information.
As may be appreciated, it is important to provide a user of a radiotelephone an ability to specify what types of SMS Broadcast messages that the user is interested in receiving. It is also important to provide the user with other SMS Broadcast-related capabilities, such as an ability to selectively enable and disable the reception of these messages, an ability to generate with the radiotelephone different indications of message-related conditions, and an ability to control the storage and display of messages.